1. Field of the Invention
The present invention relates to a particle beam irradiation system, and more particularly, to a particle beam irradiation system preferably applied to cancer treatment.
2. Description of the Related Art
When particle beam irradiation system are roughly classified, a particle beam irradiation system having a synchrotron as an accelerator (for example, see Japanese Patent Laid-Open No. 2004-358237), and a particle beam irradiation system having a cyclotron as an accelerator (for example, see Japanese Patent Laid-Open No. 2011-92444) are known as the particle beam irradiation system.
The particle beam irradiation system having the synchrotron includes an ion source, a linear accelerator, a synchrotron, a high energy beam transport system (hereinafter referred to as HEBT system), a gantry beam transport system (hereinafter referred to as GABT system), a rotary gantry, and an irradiation apparatus. A proton ion beam (or carbon ion beam) passing through a linear accelerator and being accelerated by a synchrotron to a preselected energy is emitted to an HEBT system, and passes through a GABT system, and the proton ion beam (or carbon ion beam) reaches an irradiation apparatus attached to a rotary gantry. A proton ion beam (hereinafter referred to as ion beam) is irradiated from the irradiation apparatus to an affected area of a cancer of a patient who lies on a treatment bed.
A particle beam irradiation system having a cyclotron includes an ion source, a cyclotron, an HEBT system, a GABT system, a rotary gantry, and an irradiation apparatus. The HEBT system, the GABT system, the rotary gantry, and the irradiation apparatus in the particle beam irradiation system having the cyclotron are substantially the same as the structures thereof in the particle beam irradiation system having the synchrotron. An ion beam accelerated and emitted from the cyclotron passes through the HEBT system and GABT system, and is irradiated from the irradiation apparatus to the affected area.
By the way, as illustrated in FIG. 1 of Japanese Patent Laid-Open No. H8-257023, the X ray CT apparatus has a bed and a gantry having an opening portion formed in a horizontal direction. An X ray tube generating an X ray is provided in a gantry so as to rotate around the opening portion formed in the gantry. The bed includes a bed base and a top board provided above the bed base and moving in a horizontal direction toward the opening portion. While a subject is lying on the top board, the top board as well as the subject are inserted into the opening portion, and an X ray discharged from the X ray tube is irradiated to the subject while rotating the X ray tube around the opening portion. Japanese Patent Laid-Open No. H9-140700 also describes a similar X ray CT apparatus.
These X ray CT apparatuses described in these publications are each provided with a touch sensor provided on a side surface of the gantry at the bed side and near the opening portion. When, in particular, the gantry is inclined, this touch sensor detects a contact with the touch sensor by the top board moving in the horizontal direction or the subject lying on the top board. When the touch sensor detects this contact, the movement of the top board is stopped.
Further, the particle beam irradiation system needs to fix the position of the affected area of the patient on the bed with respect to the irradiation apparatus, before the ion beam emitted by the accelerator is irradiated from the irradiation apparatus onto the affected area of the patient lying on the bed. An example of a method for fixing the position of the affected area with respect to the irradiation apparatus is described in Japanese Patent Laid-Open No. H1-209077. In the position determination of the position of the affected area in Japanese Patent Laid-Open No. H1-209077, the amount of movement of the bed for the determination of the position of the affected area is calculated by using reference image information generated on the basis of tomographic image information obtained in advance with an X ray CT apparatus before the determination of the position of the affected area and each piece of current X ray image information in two directions perpendicular to each other which are generated on the basis of X ray detection signals from an X ray detection apparatus located below the bed so as to face the X ray source provided in the irradiation apparatus while the bed on which the patient is lying is moved so that the affected area of the patient faces the irradiation apparatus before the ion beam is irradiated. The position of the affected area with respect to the irradiation apparatus is determined by manually moving the bed on the basis of the amount of movement of the bed that has been calculated. Japanese Patent Laid-Open No. H1-209077 indicates that the bed is automatically moved on the basis of the amount of movement of the bed thus calculated. It should be noted that Japanese Patent Laid-Open No. 2006-239403 also indicates that the amount of movement of the bed the rotation angle of the bed are calculated, and the bed control apparatus automatically determines the position of the affected area with respect to the irradiation apparatus on the basis of the amount of movement and the rotation angle thus calculated.